| 摘要 |
PURPOSE:To easily execute a water circulating system with freedom from maintenance over a long period of time by providing a pH control layer which brings cleaned water into contact with a material contg. a calcareous material. CONSTITUTION:The cleaned water cleaned in a filter medium tank in a 2nd aeration tank 6 rises in a sand layer from below and the transparent water free from suspended solids flows out of an outflow port 5 into a pump chamber. The cleaned water filtered in the sand layer 2 passes a crushed grain layer 3 of shell fossile and is thereby controlled in pH. This water flows out of a cleaned water outflow port 5. The pH is controlled by providing the layer of oyster shells, shell fossile, etc., above the sand filter layer. The shell fossile is less consumed and does pot require the addition over a long period of time so that the effect thereof lasts long. |
